1. Field of the Invention
The invention is related to the field of magnetic disk polishing and, in particular, to reducing burnish damage to magnetic disks caused by polishing pads such that magnetic disk production yield may be increased.
2. Statement of the Problem
Disk drives read and write magnetic flux patterns on rotating magnetic disks. Disk drives have been used for over forty years to store digital data and offer relatively low cost, high recording capacity, and rapid data retrieval. While the basic principle of reading and writing magnetic patterns on rotating disks remains about the same, components of the disk drive, particularly the read/write head and the magnetic disks, have significantly evolved.
The first magnetic disks were made by coating a rigid platter, as large as 24 inches in diameter, with magnetic particles, such as iron oxide particles, mixed in a resin. More recently, thin-film technology has been used to sputter a thin film of magnetic material on a disk. The magnetic film offers much improved magnetization when compared to the older, particulate films, thereby producing magnetic flux from a much thinner film. A thinner film also allows more narrow magnetic cells which represent a data bit to be formed. The narrower magnetic cell results in higher recording and storage densities. The magnetic thin film may be formed on a very smooth disk so as to allow the head to “fly” closer to the magnetic cells, yielding higher read-back amplitudes.
Surface roughness limits how low a head can approach the media and adds to the overall contribution of noise from the magnetic layer. Advancements in the design of recording heads, particularly the introduction of magneto-resistive (MR) heads, have caused the continued reduction in surface roughness of the magnetic disks. Present thin film media have asperities that approach 1 nm or more. In the future, as data densities increase, surface roughness is likely to be an order of magnitude less than that of present magnetic disks. Thus, advances in polishing techniques that remove asperities from the magnetic disks will likely become increasingly important.
Magnetic disk polishing via a polishing pad and polishing tape generally follows sputter deposition of magnetic layers, overcoat, and lubricant dipping. The purpose is to polish relatively high asperities on the disk surface. Polishing is a delicate process that can damage the disk by causing overcoat scratches and loosening solid particles, thereby leading to relatively poor corrosion resistance and/or decreased performance. Often, a small amount of unbonded lubricant is used to minimize polishing damage to the disk. A longer lube-to-polish delay, however, generally increases the bonded fraction of the lubricant to the magnetic disk which can lead to polishing damage to the disk.
However, too much free lubricant can also cause problems, such as lube pick-up by the head and reduced magnetic clearance. The total lubricant thickness, therefore, is often limited to reduce magnetic spacing and achieve higher areal density, thereby rendering the magnetic disk susceptible to damage during polishing. Other attempts at solving the problem are surprisingly complex. For example, in some instances, a lubricating layer is applied to the surface of a thin protective layer on a magnetic disk. Thereafter, the protective layer is polished to remove asperities from the surface thereof. The lubricant layer is then removed by solvent washing and a replacement lubricant layer is deposited on the surface of the protective layer. This multi-step process increases both time and costs for readying the magnetic disks for use in a disk drive.
Accordingly, there exists a need for lubricating the magnetic disks that deters most bonding of the lubricant to the magnetic disk until polishing is complete.